For the purpose of imparting a refreshing feeling during use or after use, cool feeling materials are often incorporated into various manufactured goods such as cosmetic products, hair care products, toiletries, bath additives and pharmaceutical products, and menthol is widely used as such a cool feeling material.
It is speculated that cooling sensation is imparted by menthol as a result of menthol having a direct action on the sensory nerve endings that exist in the skin or mucosal tissues, and studies on the mechanism concerning this impartation of cooling sensation have been underway.
First, it has been discovered that among the sensory nerves of rat, neurons that generate an inward ionic current in response to weak cooling stimuli, also exhibit the same responsiveness to menthol (Non-Patent Document 1). Through this discovery, it has been clarified that a cooling sensation caused by stimulation of menthol is induced by an inward calcium current.
Furthermore, as a receptor exhibiting responsiveness to menthol and cold stimuli, CMR-1 (cold and menthol sensitive receptor) has been identified from trigeminal neurons (Non-Patent Document 2). This receptor is called TRPM8 (Non-Patent Document 3), and it is contemplated that this receptor, which is an excitatory ion channel belonging to the TRP ion channel family, induces the calcium current described above.
Through these reports, it has been made clear that as menthol binds to TRPM8 that are present in sensory nerves, whereby generating an inward current, a cooling sensation is caused by menthol.